1. Field of the Invention
The present invention relates to a bearing sensor having magneto resistive elements and a process for bearings, in particular, to a bearing sensor and a process for bearings in which bearings are measured by applying a biasing magnetic field to the magneto resistive elements.
2. Description of the Related Art
When a current is applied to a magneto resistive element in a direction of an easy axis of magnetization, and at the same time, a magnetic field is applied in a direction perpendicular thereto, a resistance in the current direction has a magneto-resistance effect, that is, it is reduced depending on a magnetic field strength. A relationship between the resistance and the applied magnetic field strength can substantially be approximated by a quadric as shown in FIG. 24 and as follows:
R=R0(1xe2x88x92xcex1(H/Hk)2),
where reference symbol R0 denotes a resistance when no magnetic field is applied, reference symbol xcex1 denotes a resistivity variation ratio, and reference symbol Hk denotes a saturation magnetic field.
When a biasing magnetic field on the order of 1/2-Hk is applied to the magneto resistive element, there is a substantially linear relationship between an external magnetic field and the resistance. Since the maximum horizontal component of the earth magnetism is 0.4 Oe, bearings can be measured by applying an appropriate bias.
There is used a bearing sensor comprising a full bridge constituted by four magneto resistive elements 91, 92, 93, and 94 that are orthogonal to each other as shown in FIG. 25, and two bias coils 101 and 102 that are wound around a holder mounted outside of the magneto resistive elements so that two orthogonal biasing magnetic fields can be applied both at an angle of 45 degrees with respect to the current directions of the magneto resistive elements. FIG. 26 is a schematic cross-sectional view thereof, and FIG. 27 is a perspective view thereof
In measurement of bearings, a +x-direction bias is applied by one bias coil 101 (referred to as an x-direction coil) to the four magneto resistive elements 91, 92, 93, and 94 constituting the full bridge to measure an intermediate potential difference among the magneto resistive elements, and then, a xe2x88x92x-direction bias is applied by the same bias coil 101 to the magneto resistive elements to measure the intermediate potential difference among the magneto resistive elements. A difference between the intermediate potential differences measured when the +x-direction bias is applied and when the xe2x88x92x-direction bias is applied is proportional to sin xcex8, the angle xcex8 being an angle between the horizontal component of the earth magnetism and the x-axis.
Next, a +y-direction bias is applied by the other bias coil 102 (referred to as a y-direction coil) to the four magneto resistive elements 91, 92, 93, and 94 constituting the full bridge to measure an intermediate potential difference among the magneto resistive elements, and then, a xe2x88x92y-direction bias is applied by the same bias coil 102 to the magneto resistive elements to measure the intermediate potential difference among the magneto resistive elements. A difference between the intermediate potential differences measured when the +y-direction bias is applied and when the xe2x88x92y-direction bias is applied is proportional to sin(xcfx80/2-xcex8), that is, cos xcex8.
From the y-directional output Vy and the x-directional output Vx, the bearings can be measured as the direction xcex8 of the horizontal component of the earth magnetism as follows:
xcex8=a tan(Vx/Vy).
While the above description is true in terms of theory, the relationship between the magnetic field applied to the magneto resistive element and the resistance involves a hysteresis as shown in FIG. 28, rather than FIG. 24. It is said that when the applied magnetic field strength is increased, it reaches a level of saturation via the upper curve in FIG. 28, and when it is decreased from the level, it traces the lower curve.
Therefore, when measuring bearings, the saturation magnetic field is applied before the application of the biasing magnetic field in consideration of the hysteresis.
For example, as disclosed in Japanese Patent Laid-Open No. 5-157565, when measuring bearings using the bearing sensor composed of the magneto resistive elements and two orthogonal bias coils as described above, the saturation magnetic field Hk is applied in +x direction, and then the intermediate potential difference between the magneto resistive element pairs is measured while applying the +x-direction biasing magnetic field Hb. Then, the saturation magnetic field xe2x88x92Hk is applied in xe2x88x92x direction by the same bias coil, and then the intermediate potential difference between the magneto resistive element pairs is measured while applying the xe2x88x92x-direction biasing magnetic field xe2x88x92Hb. The difference between the intermediate potential differences at the time of applications of the +x-direction bias and the xe2x88x92x-direction bias thus obtained is defined as an x-direction output Vx.
Then, the saturation magnetic field is applied in the +y direction by the other bias coil, and then the intermediate potential difference between the magneto resistive element pairs is measured while applying the +y-direction biasing magnetic field. Then, the saturation magnetic field is applied in the xe2x88x92y direction by the same bias coil, and then the intermediate potential difference between the magneto resistive element pairs is measured while applying the xe2x88x92y-direction biasing magnetic field. The difference between the intermediate potential differences at the time of applications of the +y-direction bias and the xe2x88x92y-direction bias thus obtained is defined as an y-direction output Vy. Based on the Vx and Vy, bearings are measured in the manner as described above.
As the orthogonal four magneto resistive elements assembled into the full bridge described above, zigzag magneto resistive thin plates formed by etching a Ni-based alloy film deposited on one ceramic substrate may be used. Thus, the magneto resistive elements can be quite small and thin. However, since the two bias coil wound around them in x direction and y direction are provided outside the magneto resistive element bridge, the bearing sensor has, at the smallest, a thickness of the order of 3 mm and an area of the order of 10 mmxc3x9710 mm. Due to such a thickness, a wristwatch incorporating the bearing sensor has a large size.
In the procedure of measuring bearings has been explained in the above description, it is required to carry out measuring four times because the bias is applied in +x direction and xe2x88x92x direction by the x-direction coil, the bias is applied in +y direction and xe2x88x92y direction by the y-direction coil, and then calculation is carried out.
Furthermore, in order to eliminate the effect of the hysteresis of the magneto resistive element, before the biasing magnetic field is applied, the saturation magnetic field of the same direction as that of the biasing magnetic field is applied. Application of the biasing magnetic field after the application of the saturation magnetic field make the gradient of the curve for the resistance of the magneto resistive element and the magnetic field (see FIG. 28) be decreased, so that the output to be measured becomes low.
Therefore, an object of the present invention is to provide a bearing sensor of a significantly reduced thickness and area.
Furthermore, another object of the present invention is to provide a bearing sensor in which the number of applications of a current to a coil and the number of measurements are less than before.
Furthermore, another object of the present invention is to provide a process for bearings in which the number of applications of a current to a coil and the number of measurements are less than before.
Furthermore, another object of the present invention is to provide a process for bearings with an increased output.
A bearing sensor according to the present invention comprises a plane coil having at least a pair of opposed conductor sides, the opposed conductor side pair composed of a first side and a second side which are parallel to one another, and
at least one magneto resistive element pair of two magneto resistive thin plates located on a plane parallel to and adjacent to the plane coil, in which the magneto resistive element pair has a first magneto resistive thin plate and a second magneto resistive thin plate, the first magneto resistive thin plate of the magneto resistive element pair has a longitudinal direction crossing only the first side at an angle of more than 30 degrees and less than 90 degrees,
the second magneto resistive thin plate of the magneto resistive element pair has a longitudinal direction crossing only the second side at an angle of more than 30 degrees and less than 90 degrees, the longitudinal direction of the first magneto resistive thin plate is not parallel to the longitudinal direction of the second magneto resistive thin plate, and
each of the magneto resistive thin plates is electrically connected at one terminal thereof to the other magneto resistive thin plate and a voltage for measuring bearings is applied between the other terminals so that an intermediate potential is taken out from the one terminal according to bearings.
The plane coil may have an oblique section or bent portion between the opposed conductor sides parallel to each other so far as it is linear in the vicinity of points where the magneto resistive thin plates cross it. A preferable example of the plane coil suitable for the present invention is a plane coil having two pairs of opposed conductor sides. There may be an oblique section or bent R-shaped section between the two pairs of opposed conductor sides. When the two pairs of opposed conductor sides are directly connected to each other and there is no oblique or R-shaped section but the connections, the coil is referred to as a parallelogram plane coil.
More preferable plane coil used in the present invention is a coil having two pairs of the opposed conductor sides that are parallel to each other, the two pairs of the opposed conductor sides constituting at least partially four sides of a rectangle. If the two pairs of the opposed conductor sides that are parallel to each other are perpendicular to each other, the parallel coil sides constitute at least partially four sides of a rectangle. There may be an oblique section or bent R-shaped portion at the connections between the opposed conductor sides so far as the wire is linear and parallel to the wire on the other side in the vicinity of the points where it crosses the magneto resistive thin plates.
The bearing sensor may have two magneto resistive element pairs. In such a case, the longitudinal direction of one of the magneto resistive thin plates (first magneto resistive thin plate) in each of the two magneto resistive element pairs may cross only a same one side (first side) of the opposed conductor side pair of the plane coil, and the longitudinal direction of the other of the magneto resistive thin plates (second magneto resistive thin plate) in each of the two magneto resistive element pairs may cross only the opposed side (second side) of the opposed conductor side pair of the plane coil,
each of the first magneto resistive thin plates in the two magneto resistive element pairs may cross only a first side of the opposed conductor side pair, each of the second magneto resistive thin plates in the two magneto resistive element pairs may cross only a second side, opposite to the first side, of the opposed conductor side pair,
the longitudinal directions of the first magneto resistive thin plates crossing the first side of the opposed conductor side pair may not be parallel to one another, and the longitudinal directions of the second magneto resistive thin plates crossing the second side of the opposed conductor side pair may not be parallel to one another. Alternatively, the first magneto resistive thin plate of one of the two magneto resistive element pairs may cross only the first side of one of the two opposed conductor side pairs, and the second magneto resistive thin plate of the magneto resistive element pair may cross only the second side of the opposed conductor side pair, and
the first magneto resistive thin plate of the other of the two magneto resistive element pairs may cross only the first side of the other of the two opposed conductor side pairs, and the second magneto resistive thin plate of the other of the two magneto resistive element pairs may cross only the second side of the other of the two opposed conductor side pairs.
In the bearing sensor of the present invention, in the case where the two pairs of the opposed conductor sides constitute at least partially four sides of a rectangle, it is preferred that the bearing sensor has four magneto resistive element pairs, each of the magneto resistive element pairs having two magneto resistive thin plates composed of a first magneto resistive thin plate and a second magneto resistive thin plate,
in which two first magneto resistive thin plates of two of the four magneto resistive element pairs cross only the first side of one of the two opposed conductor side pairs and two second magneto resistive thin plates of the two magneto resistive element pairs cross only the second side of the same opposed conductor side pair,
while two first magneto resistive thin plates of the other two of the four magneto resistive element pairs cross only the first side of the other opposed conductor side pair and two second magneto resistive thin plates of the other two magneto resistive element pairs cross only the second side of the other opposed conductor side pair, the longitudinal directions of the two magneto resistive thin plates crossing the same side of the plane coil being not parallel to one another.
In the bearing sensor of the present invention, it is preferred that the angle at which the longitudinal direction of each of the magneto resistive thin plates crosses a side of the opposed conductor side pair of the plane coil is more than or equal to 45 degrees and less than 90 degrees, and the variation in the crossing is within +/xe2x88x925 degrees. More preferably, the crossing angle is about 45 degrees.
In the bearing sensor of the present invention, it is preferred that the longitudinal direction of one of the magneto resistive thin plates in each of the magneto resistive element pairs is perpendicular to the longitudinal direction of the other of the magneto resistive thin plates in the same magneto resistive element pair. In addition, it is preferred that the longitudinal directions of the two magneto resistive thin plates crossing one side of the plane coil is perpendicular to each other.
As the plane coil used in the present invention, a cross-shaped plane coil wound along outside of a cross-shaped plane and having four pairs of the opposed conductor sides may be used, in which each side of the opposed conductor side pair is located between a top corner and a bottom corner on a side of a protrusion of the cross-shaped plane, the first side of each of the opposed conductor side pairs is parallel to the second side of the same opposed conductor side pair,
the sides of two of the four opposed conductor side pairs is parallel to one another and perpendicular to the sides of the other two of the four opposed conductor side pairs.
In such a case, the bearing sensor has two magneto resistive element pairs, each of the magneto resistive element pairs having two magneto resistive thin plates composed of a first magneto resistive thin plate and a second magneto resistive thin plate.
Alternatively, the bearing sensor may have four magneto resistive element pairs, each of the magneto resistive element pairs having two magneto resistive thin plates composed of a first magneto resistive thin plate and a second magneto resistive thin plate, in which the first magneto resistive thin plates in two of the four magneto resistive element pairs cross, respectively, only the first sides, which are parallel to one another, in first two of the four opposed conductor side pairs, and the second magneto resistive thin plates in the two magneto resistive element pairs cross, respectively, only the second sides in the first two opposed conductor side pairs which are parallel to one another,
while the first magneto resistive thin plates in the other two of the four magneto resistive element pairs cross, respectively, only the first sides of the other two of the four opposed conductor side pairs which are perpendicular to the first two opposed conductor side pairs and
the second magneto resistive thin plates of the other two magneto resistive element pairs cross, respectively, only the second sides of the other two of the four opposed conductor side pairs, and
the longitudinal direction of the first magneto resistive thin plate of the magneto resistive element pair at a protrusion of the cross-shaped plane coil is not parallel to the longitudinal direction of the first magneto resistive thin plate of the magneto resistive element pair at the opposite protrusion, and the longitudinal direction of the second magneto resistive thin plate of the magneto resistive element pair at the protrusion is not parallel to the longitudinal direction of the second magneto resistive thin plate of the magneto resistive element pair at the opposite protrusion.
In the bearing sensor having the cross-shaped plane coil of the present invention, it is preferred that the angle at which the longitudinal direction of each of the magneto resistive thin plates crosses a side of the opposed conductor side pair of the plane coil is more than or equal to 45 degrees and less than 90 degrees, and the variation in the crossing is within +/xe2x88x925 degrees. More preferably, the crossing angle is about 45 degrees.
In the bearing sensor of the present invention, it is preferred that the longitudinal direction of one of the magneto resistive thin plates in each of the magneto resistive element pairs is perpendicular to the longitudinal direction of the other magneto resistive thin plates in the same magneto resistive element pair.
The bearing sensor of the present invention may comprise a plane coil having two pairs of opposed conductor sides parallel to one another, the two pairs of the opposed conductor sides constituting at least partially four sides of a rectangle, the opposed conductor side pair composed of a first side and a second side, and
two magneto resistive element planes located at both sides of the plane coil and being parallel to and adjacent to the plane coil,
in which each of the magneto resistive element planes includes four magneto resistive thin plates having a longitudinal direction crossing only a single side of the opposed conductor side pair at an angle of more than 30 degrees and less than 90 degrees, two magneto resistive thin plates of which the longitudinal directions cross a pair of the opposed conductor sides and are not parallel to one another constitute a magneto resistive element pair of the magneto resistive thin plates having a first magneto resistive thin plate and a second magneto resistive thin plate, the first and the second magneto resistive thin plates being applied opposite magnetic fields by a DC current flowing through the plane coil,
each of the magneto resistive thin plates is electrically connected at one terminal thereof to the other and a voltage for measuring bearings is applied between the other terminals so that an intermediate potential output is taken out from the one terminal according to bearings.
In this case again, it is preferred that the angle at which the longitudinal direction of each of the magneto resistive thin plates crosses a side of the opposed conductor side pair of the plane coil is more than or equal to 45 degrees and less than 90 degrees, and the variation in the crossing is within +/xe2x88x925 degrees. More preferably, the crossing angle is about 45 degrees.
For this bearing sensor, it is preferred that the longitudinal direction of one of the magneto resistive thin plates in each of the magneto resistive element pairs is perpendicular to the longitudinal direction of the other of the magneto resistive thin plates in the same magneto resistive element pair, and
the longitudinal directions of two magneto resistive thin plates between which a side of the opposed conductor side pair is put are perpendicular to one another.
The bearing sensor of the present invention may comprise a magneto resistive element plane, and two plane coils located on both sides of the magneto resistive element plane and being parallel to and adjacent to the magneto resistive element plane,
in which each of the two plane coils has at least two pairs of opposed conductor sides, the two pairs of the opposed conductor sides constituting at least four sides of a rectangle, the opposed conductor side pair composed of a first side and a second side which are parallel to one another,
the magneto resistive element plane has two magneto resistive thin plates per a side of the opposed conductor side pair of the plane coils, the two magneto resistive thin plates having longitudinal directions crossing only the side of the opposed conductor side pair at an angle of more than 30 degrees and less than 90 degrees and being not parallel to one another,
a magneto resistive element pair is composed of one of the magneto resistive thin plates crossing the first side of the opposed conductor side pair of the two plane coils and the magneto resistive thin plate crossing the second side of the opposed conductor side pair of the two plane coils and being not parallel to the longitudinal direction of the one of the magneto resistive thin plates, and
each of the magneto resistive thin plates is electrically connected at one terminal thereof to the other and a voltage for measuring bearings is applied between the other terminals so that an intermediate potential output is taken out from the one terminal according to bearings.
In the bearing sensor, it is preferred that the angle at which the longitudinal direction of each of the magneto resistive thin plates crosses a side of the opposed conductor side pair of the plane coil is more than or equal to 45 degrees and less than 90 degrees. More preferably, the magneto resistive element plane has two magneto resistive thin plates per a side of the opposed conductor side pair of the plane coils, the two thin plates have longitudinal directions crossing only the side of the opposed conductor side pair at an angle of about 45 degrees and are perpendicular to one another, and
longitudinal directions of two thin plates of a magneto resistive element pair are perpendicular to one another.
In the process for bearings according to the present invention, the bearing sensors described above are used. This process comprises the steps of:
passing a first DC current through the plane coil to apply to the magneto resistive thin plates a DC magnetic field enough to saturate a magnetization of the magneto resistive thin plates in the longitudinal direction of each of the magneto resistive thin plates;
passing a first biasing DC current opposite to the first DC current of a predetermined strength through the plane coil to apply a biasing DC magnetic field perpendicular to the longitudinal direction;
applying a voltage for measuring bearings between the other terminals of the magneto resistive element pairs to take out a first intermediate potential from the connected terminals of the magneto resistive element pairs during the application of the biasing DC magnetic field;
passing a second DC current opposite to the first DC current through the plane coil to apply to the magneto resistive thin plates a DC magnetic field enough to saturate a magnetization of the magneto resistive thin plates in the longitudinal direction of each of the magneto resistive thin plates;
passing a second biasing DC current opposite to the second DC current of a predetermined strength through the plane coil to apply a biasing DC magnetic field perpendicular to the longitudinal direction;
applying a voltage for measuring bearings between the other terminals of the magneto resistive element pairs to take out a second intermediate potential from the connected terminals of the magneto resistive element pairs during the application of the biasing DC magnetic field; and
obtaining a difference between the first and the second intermediate potentials to measure bearings from the difference.
In the case where a bearing sensor having two or four magneto resistive element pairs is used, instead of the first and the second intermediate potentials, a first and a second intermediate potential differences between two magneto resistive element pairs crossing a same opposed conductor side pair are taken out, and a difference between the first and the second intermediate potential differences is obtained to measure bearings from the difference.
In the bearing sensor used for measuring bearings according to the present invention, it is preferred that the plane coil is a rectangle, the longitudinal direction of one of the magneto resistive thin plates in each of the magneto resistive element pairs is perpendicular to the longitudinal direction of the other of the magneto resistive thin plates in the same magneto resistive element pair, and
the longitudinal directions of the magneto resistive thin plates crossing a same side of the plane coil are perpendicular to one another.